1. Field of the Invention
The present invention relates to a metal belt-type continuously variable transmission including a metal belt reeved around a drive pulley and a driven pulley, and more particularly, to a process for presuming a power-transmitted state in such a metal belt-type continuously variable transmission and a process for controlling the axial thrust using such process.
2. Description of the Related Art
To determine a friction coefficient .mu. between a pulley and a block in a metal belt-type continuously variable transmission, conventionally, as described in Japanese Patent Application Laid-open No. 6-117530, for example, the axial thrusts of a drive pulley and a driven pulley are gradually decreased while operating the transmission at a given speed ratio, and the friction coefficient .mu. is calculated according to the following equation based on the axial thrust at a moment when slipping is generated between a metal belt and the pulley: EQU Q=T cos .alpha./2.mu.R
wherein Q is the axial thrust of a pulley which has slipped; T is the torque of the pulley which has slipped; R is the pitch radius of the pulley which has slipped; and .alpha. is the inclination angle of the V-bevel face of the pulley.
If an attempt is made to determine the friction coefficient .mu. using the conventional method, it is necessary to produce slipping between the metal belt and the pulley at a predetermined relative speed, and the following problem is encountered: it is difficult to control the axial thrust of the pulley, so that the slip amount does not exceed a predetermined value. In many cases, the slip amount is abruptly increased at the moment when slipping is generated, whereby the metal belt and the pulley are fused, resulting in a non-normal friction coefficient, and the metal belt or the like is broken.